An Invoice Table

• For other objects, it is not so easy to come up with an equivalent database table structure
• Consider an invoice; each invoice object contains a reference to a customer object:

  public class Invoice
  {
     . . .
     private int invoiceNumber;
     private Customer theCustomer;
     . . .
  }

• You might consider simply entering all the customer data into the invoice tables
  • It is wasteful
  • It is dangerous; on a change, you can forget to update all occurrences
• In a Java program, neither of these problems occur
  • Multiple Invoice objects can contain references to a single Customer